After that - all bets are off...
The United States could easily annihilate Syrian and even Russian air defenses—and airpower—inside Syria. Moscow—even with the fearsome capabilities of its S-400 air and missile defense system—is not able to defeat the U.S. Air Force’s fleet of stealthy Lockheed Martin F-22 Raptors, which are able to fly inside zones protected by those system and defeat them. In fact, defeating advanced air defenses is one of the Raptor’s primary missions. Nor would Russian Su-30SM or Su-35S Flankers survive long against the Raptor, which was specifically designed to counter advanced next-generation Soviet fighters that ultimately never materialized.That’s especially true in a conflict where the lines are blurry and there are no clear-cut good guys—where even so-called “moderate” rebels backed by the U.S. government are beheading children.
The problem is that the United States cannot know for certain if Moscow will idly stand by while American forces attack Syrian forces. Moreover, it is unclear how many Russian military advisors are embedded with Syrian forces and where those instructors are located. Some Russian advisors are present and operating within the ranks of the Syrian military, and if Washington launches a strike, those forces could be caught in the crossfire. However, Russian rhetoric suggests that Moscow won’t simply allow Bashar al-Assad’s forces to be destroyed. Russian foreign ministry spokeswoman Maria Zakharova was quoted by the Russian media saying that U.S. intervention against Assad “will lead to terrible, tectonic consequences not only on the territory of this country but also in the region on the whole.”
If the U.S. military does intervene in Syria, and Russian and Syrian forces fight back, American F-22s would likely be able to quickly eliminate the Russian S-400, Pantsir-S1 as well as Russia’s Su-30, Su-35s and Su-34s with relative ease. Conventional U.S. fourth-generation fighters such as the F-15, F-16 and F/A-18 would have to wait until the Russian-built air defenses—which, given the S-400’s nearly 250 mile coverage radius, encompass nearly the entire Syrian landmass—were cleared by stealth aircraft such as the Raptor and the Northrop Grumman B-2 Sprit strategic bomber. It is not clear if the long-range 40N6 is operational, but regardless, actions can have unintended consequences.
Russia might not limit its retaliation to just American and NATO forces in Syria. Given Moscow’s arsenal of Kaliber-NK cruise missiles and long-range bombers and submarines, the Kremlin has options to strike back across a huge geographic range. It is not outside realm of the possible that Russia would hit back at U.S. bases in Qatar, United Arab Emirates or Turkey using long-range precision-guided cruise missiles. The Russian Black Sea fleet and the Caspian Sea flotilla can easily hit such targets. Then there is Moscow’s formidable bomber fleet which can target the continental United States itself.
Thus, while it is easy to start a conflict with Russia and Syria, a shooting war could easily escalate out of control. It might be prudent to exercise restraint before launching a new war—against a nuclear-armed power—that the American people don’t necessarily want to fight.